250 lines
10 KiB
Plaintext
250 lines
10 KiB
Plaintext
SPDX-License-Identifier: GPL-2.0+
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/*
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* Copyright 2010-2011 Calxeda, Inc.
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*/
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The 'pxe' commands provide a near subset of the functionality provided by
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the PXELINUX boot loader. This allows U-Boot based systems to be controlled
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remotely using the same PXE based techniques that many non U-Boot based servers
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use.
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Commands
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========
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pxe get
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-------
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syntax: pxe get
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follows PXELINUX's rules for retrieving configuration files from a tftp
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server, and supports a subset of PXELINUX's config file syntax.
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Environment
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-----------
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'pxe get' requires two environment variables to be set:
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pxefile_addr_r - should be set to a location in RAM large enough to hold
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pxe files while they're being processed. Up to 16 config files may be
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held in memory at once. The exact number and size of the files varies with
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how the system is being used. A typical config file is a few hundred bytes
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long.
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bootfile,serverip - these two are typically set in the DHCP response
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handler, and correspond to fields in the DHCP response.
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'pxe get' optionally supports these two environment variables being set:
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ethaddr - this is the standard MAC address for the ethernet adapter in use.
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'pxe get' uses it to look for a configuration file specific to a system's
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MAC address.
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pxeuuid - this is a UUID in standard form using lower case hexadecimal
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digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
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it to look for a configuration file based on the system's UUID.
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File Paths
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----------
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'pxe get' repeatedly tries to download config files until it either
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successfully downloads one or runs out of paths to try. The order and
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contents of paths it tries mirrors exactly that of PXELINUX - you can
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read in more detail about it at:
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http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
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pxe boot
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--------
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syntax: pxe boot [pxefile_addr_r]
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Interprets a pxe file stored in memory.
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pxefile_addr_r is an optional argument giving the location of the pxe file.
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The file must be terminated with a NUL byte.
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Environment
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-----------
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There are some environment variables that may need to be set, depending
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on conditions.
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pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
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an environment variable named pxefile_addr_r must be supplied. This is
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typically the same value as is used for the 'pxe get' command.
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bootfile - typically set in the DHCP response handler based on the
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same field in the DHCP respone, this path is used to generate the base
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directory that all other paths to files retrieved by 'pxe boot' will use.
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If no bootfile is specified, paths used in pxe files will be used as is.
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serverip - typically set in the DHCP response handler, this is the IP
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address of the tftp server from which other files will be retrieved.
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kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
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store the kernel(or FIT image) and initrd it retrieves from tftp. These
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locations will be passed to the bootm command to boot the kernel. These
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environment variables are required to be set.
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fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
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retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
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pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
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will be passed to bootm command to boot the kernel.
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fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
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command if it is set and 'fdt_addr_r' is not passed to bootm command.
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pxe file format
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===============
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The pxe file format is nearly a subset of the PXELINUX file format; see
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http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
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commands - global commands, and commands specific to labels. Lines begining
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with # are treated as comments. White space between and at the beginning of
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lines is ignored.
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The size of pxe files and the number of labels is only limited by the amount
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of RAM available to U-Boot. Memory for labels is dynamically allocated as
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they're parsed, and memory for pxe files is statically allocated, and its
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location is given by the pxefile_addr_r environment variable. The pxe code is
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not aware of the size of the pxefile memory and will outgrow it if pxe files
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are too large.
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Supported global commands
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-------------------------
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Unrecognized commands are ignored.
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default <label> - the label named here is treated as the default and is
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the first label 'pxe boot' attempts to boot.
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menu title <string> - sets a title for the menu of labels being displayed.
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menu include <path> - use tftp to retrieve the pxe file at <path>, which
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is then immediately parsed as if the start of its
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contents were the next line in the current file. nesting
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of include up to 16 files deep is supported.
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prompt <flag> - if 1, always prompt the user to enter a label to boot
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from. if 0, only prompt the user if timeout expires.
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timeout <num> - wait for user input for <num>/10 seconds before
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auto-booting a node.
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label <name> - begin a label definition. labels continue until
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a command not recognized as a label command is seen,
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or EOF is reached.
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Supported label commands
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------------------------
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labels end when a command not recognized as a label command is reached, or EOF.
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menu default - set this label as the default label to boot; this is
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the same behavior as the global default command but
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specified in a different way
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kernel <path> - if this label is chosen, use tftp to retrieve the kernel
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(or FIT image) at <path>. it will be stored at the address
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indicated in the kernel_addr_r environment variable, and
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that address will be passed to bootm to boot this kernel.
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For FIT image, The configuration specification can be
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appended to the file name, with the format:
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<path>#<conf>[#<extra-conf[#...]]
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It will passed to bootm with that address.
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(see: doc/uImage.FIT/command_syntax_extensions.txt)
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It useful for overlay selection in pxe file
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(see: doc/uImage.FIT/overlay-fdt-boot.txt)
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append <string> - use <string> as the kernel command line when booting this
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label.
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initrd <path> - if this label is chosen, use tftp to retrieve the initrd
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at <path>. it will be stored at the address indicated in
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the initrd_addr_r environment variable, and that address
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will be passed to bootm.
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fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
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at <path>. it will be stored at the address indicated in
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the fdt_addr_r environment variable, and that address will
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be passed to bootm.
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fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob
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relative to <path>. If the fdtfile environment variable
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is set, <path>/<fdtfile> is retrieved. Otherwise, the
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filename is generated from the soc and board environment
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variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
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If the fdt command is specified, fdtdir is ignored.
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localboot <flag> - Run the command defined by "localcmd" in the environment.
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<flag> is ignored and is only here to match the syntax of
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PXELINUX config files.
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Example
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-------
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Here's a couple of example files to show how this works.
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------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
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menu title Linux selections
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# This is the default label
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label install
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menu label Default Install Image
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kernel kernels/install.bin
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append console=ttyAMA0,38400 debug earlyprintk
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initrd initrds/uzInitrdDebInstall
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# Just another label
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label linux-2.6.38
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kernel kernels/linux-2.6.38.bin
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append root=/dev/sdb1
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# The locally installed kernel
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label local
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menu label Locally installed kernel
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append root=/dev/sdb1
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localboot 1
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-------------------------------------------------------------
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------------/tftpboot/pxelinux.cfg/default-------------------
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menu include pxelinux.cfg/menus/base.menu
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timeout 500
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default linux-2.6.38
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-------------------------------------------------------------
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When a pxe client retrieves and boots the default pxe file,
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'pxe boot' will wait for user input for 5 seconds before booting
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the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
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to be downloaded, and boot with the command line "root=/dev/sdb1"
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Differences with PXELINUX
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=========================
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The biggest difference between U-Boot's pxe and PXELINUX is that since
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U-Boot's pxe support is written entirely in C, it can run on any platform
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with network support in U-Boot. Here are some other differences between
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PXELINUX and U-Boot's pxe support.
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- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
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in RFC 5071, but could be extended to do so.
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- when U-Boot's pxe fails to boot, it will return control to U-Boot,
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allowing another command to run, other U-Boot command, instead of resetting
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the machine like PXELINUX.
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- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
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only uses U-Boot.
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- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
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does, only a simple text based menu using the commands described in
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this README. With PXELINUX, it's possible to have a graphical boot
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menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
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a more robust menuing system like that of PXELINUX's.
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- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work
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with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
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- U-Boot's pxe only recognizes a single file on the initrd command line. It
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could be extended to support multiple.
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- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
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disk boot - it will do whatever is defined in the 'localcmd' env
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variable. And since it doesn't support a full UNDI/PXE stack, the
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type field is ignored.
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- the interactive prompt in U-Boot's pxe only allows you to choose a label
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from the menu. If you want to boot something not listed, you can ctrl+c
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out of 'pxe boot' and use existing U-Boot commands to accomplish it.
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